The present invention relates to a device for longitudinally cutting web material, especially paper and cardboard webs with at least one rotating circular knife pair consisting of a freely rotating point knife that enters the material during the cutting process and of a pot knife that rests on a power-rotated hub element.
A longitudinal cutting device of the aforesaid type is known for example from U.S. Pat. No. 4,210,045. Devices of that type, in which the point and pot knives can, if necessary, be adjusted with setting mechanisms to a particular desired cutting position, operate satisfactorily in themselves. Still, problems arise when the pot knives have to be reground or replaced. The width of the knife, and hence the overall width of the cut, changes when a knife is reground.
It is especially expensive and time-consuming in double longitudinal cutting devices, in which two circular-knife pairs operate superimposed, to adjust the knife units in relation to each other when new or reground knife blades are mounted. The same is true of programmed longitudinal cutting devices, in which the knife units are strictly motor-adjusted. In this case the basic or zero position of the units must always be corrected to accord with the amount of material ground off of the blade.